Definition of "whaup"

It looks eerie at bright midday, when the sun is shining and whaups are crying among the seaweeds; but think what it was on that awesome night, with the Powers of Darkness brooding over it like a cloud!

1902, John Buchan, The Outgoing of the Tide

A whaup flapped up with its liquid, rising cry and he found himself wheeling round in in a dizziness of blue as he tried to follow its flight.

2022, Liam McIlvanney, The Heretic, page 368